Investigation of flows over airfoils operating at low Reynolds numbers and development of effective flow control strategies.

最近小型化机械系统的进步，如中小型风力涡轮机和无人驾驶飞行器，引起了人们对低雷诺数空气动力学的更大兴趣。在这些应用中，翼型的弦雷诺数约为50,000到500,000，并且翼型的性能与经典空气动力学中所期望的有很大的不同。具体地说，层流边界层分离通常发生在翼型的上表面，这会降低升力，增加阻力。分离剪切层的行为和分离流区的范围是决定翼型性能退化程度的主要因素。翼型的几何形状优化和流动控制可用于延迟分离和/或最小化分离的流动区域的尺寸，从而增强升力和减少阻力。然而，实施这些方法需要对流动物理有深入的了解。研究的主要目的是加深对低雷诺数下翼型流动发展的了解，并开发有效的主动反馈流动控制方法来提高翼型的性能。为了达到这些目标，将在承受不利压力梯度的平板和翼型模型上进行新颖的实验研究，前者的几何形状用作翼型上的流动模型，同时便于进行广泛的参数研究。实验将在自适应壁风洞中进行，利用高速流动显示、速度测量和新开发的涉及嵌入式麦克风的时间分辨表面测量技术。这种独创的实验方法组合将为低雷诺数下翼型的流动发展提供独特的见解。这些研究成果除了对流体力学基础研究具有重要意义外，还将对实际工程应用产生重大影响。这些发现对于为小型化机械系统设计更有效的升力面和实施有效的流量控制策略以提高系统性能将是至关重要的。

Recent advancements in miniaturized mechanical systems, such as small-to-medium scale wind turbines and unmanned aerial vehicles, have brought about an increased interest in low Reynolds number aerodynamics. In these applications, airfoils operate at chord Reynolds numbers ranging from about 50,000 to 500,000, and airfoil performance differs substantially from that expected in classical aerodynamics. Specifically, laminar boundary layer separation often takes place on the upper surface of the airfoil, which decreases lift and increases drag. The behaviour of the separated shear layer and the extent of a separated flow region are major factors that determine the degree of degradation in airfoil performance. Airfoil geometry optimization and flow control can be used to delay separation and/or to minimize the size of the separated flow region, thereby enhancing lift and decreasing drag. However, implementing these methods requires in-depth knowledge of the flow physics. The main objectives of the proposed research are to improve understanding of flow development over airfoils at low Reynolds numbers and to develop effective active-feedback flow control methods for enhancing airfoil performance. To meet these objectives, novel experimental studies will be performed on a flat-plate subjected to an adverse pressure gradient and on an airfoil model, with the former geometry serving as a model of flow over an airfoil while facilitating extensive parametric investigations. Experiments will be performed in an adaptive-wall wind tunnel utilizing high-speed flow visualization, velocity measurements, and a newly developed time-resolved surface measurement technique involving embedded microphones. This original combination of experimental methods will provide unique insight into the flow development over an airfoil at low Reynolds numbers. In addition to their significance for fundamental fluid mechanics, the research results will have a strong impact on practical engineering applications. The findings will be essential for designing more efficient lifting surfaces for miniaturized mechanical systems and implementing effective flow control strategies for improving system performance.